JPH0658672A - Lime crucible and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a lime crucible and manufacturing method therefor for manufacturing a metal or an alloy, such as Ti or an TiAi alloy, wherein an oxygen containing amount is low, without sacrificing excellent heat resistance and corrosion resistance of the lime crucible. CONSTITUTION:A lime crucible is formed of 100 pts.wt. potassium oxide and 8-25 pts.wt. potassium fluoride and has apparent porosity of 12% or less. In manufacture of the lime crucible, an uniform mixture of 100 pts.wt. potassium oxide powder and 8-30 pts.wt. potassium fluoride powder is press-molded in a crucible shape. The produced molded product is burnt at a temperature of 1300-1550 deg.C until apparent porosity goes below 12%.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a lime-based crucible, in particular,
The present invention relates to a lime-based crucible for melting metal, which is suitable for manufacturing a metal material having a low oxygen content, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Lime (calcia, CaO) type crucibles are
It has a high melting point, has dephosphorization and desulfurization effects, and has excellent properties as a crucible with a low dissociated oxygen pressure at high temperatures.
Therefore, it is used as a crucible for steelmaking that requires high quality steel, and as a crucible for melting a metal having a strong oxidizing power and a high melting point, such as titanium (Ti) or a Ti alloy.

Titanium-aluminum (TiAl) -based intermetallic compounds have been attracting attention as a lightweight heat-resistant material to replace Ni-based alloys because they have low density (3.8) and excellent high-temperature strength. Since Ti and TiAl-based alloys are remarkably active in a molten state, when Ti or TiAl-based alloy is melted using a crucible, Ti or TiAl-based alloy reacts with the crucible or absorbs gas, resulting in Ti or Ti The TiAl-based alloy is contaminated and the hardness increases, which deteriorates ductility and workability. Therefore, melting methods such as consumable electrode arc melting, plasma arc melting, plasma beam melting, and induction skull melting are used for melting high-quality Ti and TiAl alloys.

However, in order to industrially produce Ti or TiAl alloys, it is desirable to employ a melting method by high frequency induction heating or resistance heating using a crucible. Therefore, lime-based crucibles for melting Ti and TiAl-based alloys have been studied, and some lime-based crucibles have been proposed.

For example, JP-A-61-72678 discloses that electrofused calcia powder contains 2 to 8% by weight of vegetable oil and 2 to
Disclosed is a method for producing a calcareous crucible for melting metal, in which 8% by weight of calcium fluoride is added, kneaded, press-molded, and fired in a temperature range of 1000 to 1800 ° C. In the above-mentioned patent publication, in this method for producing a crucible, calcium fluoride is added as a sintering aid, and since calcium fluoride causes thermal decomposition by heating at 1000 ° C. or higher, fluorine is not generated. The remaining calcium ions that have been scattered out of the system react with oxygen in the atmosphere to become CaO, which is the same as the main raw material (see the above publication, page 2, lower right column, lines 7 to 11), and 8% by weight. If calcium fluoride is added in excess, undecomposed CaF ₂ will remain in a large amount and decomposed gas will be generated during use of the crucible to make the dissolution unstable (the above-mentioned page 4, upper left column, lines 7-9). Reference) is described. From these facts, the crucible manufactured by the method described in JP-A-61-72678 has a much smaller amount of fluoride than the amount of calcium fluoride added as a raw material, even if it remains. It is considered that it contains only calcium oxide.

Further, Japanese Patent Laid-Open No. 61-72678 describes that the crucible produced has an apparent porosity of 12.5% and 13.0% (see Table 1 on page 5 of the above publication). The oxygen content of the re-solidified alloy obtained by melting a titanium alloy in a vacuum high frequency induction furnace using this crucible is 0.
It is described as 10% by weight and 0.12% by weight (see the above publication, page 5, table 2). Generally, if the oxygen content in the TiAl-based alloy is large, the TiAl-based alloy becomes hard, which is not preferable, and the oxygen content in the TiAl-based alloy is 0.0
It is desirable to set it to 8% by weight or less. Therefore, JP-A-6
The crucible manufactured by the method described in JP-A-1-72678 cannot be said to be sufficiently satisfactory.

[0007] In "Iron and Steel", No. 78 (1992), No. 4, pages 172-179, there is disclosed a crucible in which 5 to 20% by weight of CaF ₂ is added as a binder to CaO. It is described that the rate was 13 to 16% (see Table 1 on page 173 of the above document).
Then, it is described that the oxygen content in the obtained TiAl-based alloy when the TiAl-based alloy was melted using the CaO-CaF ₂ crucible was 0.13 to 0.11% by weight ( (See page 175 of the above document). Therefore, the CaO-CaF ₂ crucible described in this document cannot be said to be sufficiently satisfactory.

[0008]

The object of the present invention is to provide a metal or alloy having a low oxygen content, particularly Ti or T, without sacrificing the excellent heat resistance and corrosion resistance of the lime crucible.
An object of the present invention is to provide a lime-based crucible capable of producing an iAl-based alloy and a method for producing the same.

[0009]

DISCLOSURE OF THE INVENTION The inventors of the present invention have taken advantage of the unique characteristic of lime crucibles, which are extremely excellent in heat resistance and corrosion resistance, and have a low oxygen content in metals or alloys having excellent characteristics, particularly Intensive research has been done on producing crucibles that can be used to produce Ti or TiAl based alloys. As a result, they have found that the object of the present invention can be achieved by a lime crucible containing calcium fluoride in a specific range and having a low porosity.

The present invention is a lime crucible characterized by comprising 100 parts by weight of calcium oxide and 8 to 25 parts by weight of calcium fluoride, and having an apparent porosity of 12% or less.

Another aspect of the present invention is a calcium oxide powder 100.
A mixture of 1 part by weight and 8 to 30 parts by weight of calcium fluoride powder was press-molded into a crucible, and the resulting molded body was heated to 130
A method for producing a lime-based crucible, which comprises firing at a temperature of 0 to 1550 ° C. until the apparent porosity becomes 12% or less.

Preferred embodiments of the present invention are as follows.

(1) The lime crucible as described above, which has an apparent porosity of 8% or less.

(2) The calcium oxide powder is 3 mm
A powder having the following particle size, containing 10 to 40% by weight of particles having a particle size of 1.0 to 0.5 mm and containing 20 to 50% by weight of particles having a particle size of 0.15 mm or less. The method for producing a lime-based crucible as described above, characterized by being present.

(3) The above calcium fluoride is 150 μm
The method for producing a lime crucible as described above, which is a powder having a particle size of m or less.

(4) The above-mentioned molded product has an apparent porosity of 8%.
The method for producing a lime-based crucible as described above, which comprises firing until the temperature becomes as follows.

The lime crucible of the present invention is characterized by having a composition of 100 parts by weight of calcium oxide and 8 to 25 parts by weight of calcium fluoride, and having an apparent porosity of 12% or less. Is.

In this specification, the apparent porosity is defined by JIS
It is a value measured according to Z8807-1976.

The lime type crucible of the present invention is disclosed in Japanese Patent Application Laid-Open No. 61-7.
It differs from the calcareous crucible produced by the method disclosed in Japanese Patent No. 2678 in that it has a high calcium fluoride content and a low apparent porosity. Further, as is apparent from the examples described below, when the TiAl-based alloy is melted using the lime-based crucible of the present invention, the oxygen content in the TiAl-based alloy produced is found in JP-A-61-72678. The two crucibles are also different from each other in that the crucible disclosed in the publication has a remarkably excellent effect as compared with the case of using the crucible.

In Japanese Patent Application Laid-Open No. 61-72678, calcium fluoride causes thermal decomposition by heating at 1000 ° C. or higher, so that fluorine is scattered out of the system, and the remaining calcium ions react with oxygen in the atmosphere. To be the same CaO as the main raw material (see the above publication, page 2, lower right column, lines 7 to 11),
And if more than 8% by weight of calcium fluoride is added, a large amount of undecomposed CaF ₂ remains, and decomposition gas is generated during the use of the crucible, resulting in unstable dissolution (Patent Document 4 above).
(See upper left column, lines 7 to 9).

However, according to the studies by the present inventors, even if a molded body produced from a mixture of calcium oxide powder and calcium fluoride powder of 8% by weight or more of calcium oxide powder is fired at 1300 to 1550 ° C. Almost no decomposition (causing, scattering, etc.) of calcium fluoride occurs, and most (approximately 80% or more) of calcium fluoride in the powder mixture of the raw materials remains in the produced lime crucible (calcined compact). , And contributed to the decrease of the apparent porosity of lime crucible. Furthermore, calcium fluoride does not react with Ti (the above-mentioned document: “Iron and Steel” 78th year (199
2) No. 4, p. 172), even if calcium fluoride remains in the lime crucible, it does not adversely affect the metal to be melted, particularly Ti and TiAl alloys, and Ti and Ti having a small oxygen content. It was found that the TiAl-based alloy can be produced.

Further, in "Iron and Steel", No. 78 (1992), No. 4, pp. 172-179, a TiAl-based alloy was prepared by using a crucible prepared by adding 5 to 20% by weight of CaF ₂ as a binder to CaO. The Ti obtained when the alloy was melted
Oxygen content in Al-based alloy is 0.13 to 0.11% by weight
It is described that the effect of suppressing the oxygen content of the TiAl alloy was not recognized. However, the crucible described in this document has a porosity of 13 to 16%, and has a larger apparent porosity than the lime-based crucible of the present invention, which means that oxygen in the TiAl-based alloy is high. It is speculated that this may be one of the reasons why the content is not reduced.

In any case, the lime crucible of the present invention is
It is a novel one completely different from the lime-based crucibles disclosed in the above-mentioned patent publications and documents, and exhibits excellent effects.

The lime crucible of the present invention has a composition of 100 parts by weight of calcium oxide and 8 to 25 parts by weight of calcium fluoride, preferably 10 to 20 parts by weight. When the amount of calcium fluoride is smaller than the above range, the apparent porosity of the lime crucible becomes large, and when the amount of calcium fluoride is larger than the above range, the mechanical strength of the lime crucible at high temperature is lowered.

The lime crucible of the present invention has a structure in which the surface of granular calcium oxide is coated with calcium fluoride, and the granular calcium oxide is adhered by calcium fluoride.

In the lime-based crucible of the present invention, when the particles of calcium oxide are reduced, the apparent porosity of the lime-based crucible decreases, but the physical properties of the lime-based crucible, particularly the thermal shock resistance, tend to decrease. . In order to keep the physical properties of the lime-based crucible high while at the same time reducing the apparent porosity, it is necessary for the calcium oxide to have the form of granules with a rather broad particle size distribution. Generally, particles of calcium oxide have a particle size of 3 mm or less and contain 10 to 40% by weight of particles having a particle size of 1.0 to 0.5 mm and a particle size of 0.15 mm or less. It is preferable that the particles have a particle size distribution such that the particles contained therein are contained in an amount of 20 to 50% by weight.

The apparent porosity of the lime crucible of the present invention is
It is preferably 8% or less. The smaller the apparent porosity of a lime-based crucible, the more it is possible to reduce the oxygen content in metallic materials produced using the crucible, in particular TiAl-based alloys.

The lime-based crucible of the present invention, even when it is repeatedly used to dissolve a metal material, particularly Ti or TiAl-based alloy, does not infiltrate the molten metal into the crucible and is hardly damaged at all. Therefore, it can be repeatedly used to dissolve the metal material. Therefore, the lime-based crucible of the present invention is a lime-based crucible whose wall thickness can be reduced, which is lightweight and easy to handle. Further, the lime-based crucible of the present invention can reduce the oxygen content in the metal material after melting, and can further reduce the oxygen content in the metal material after melting by repeated use.

The method for producing a lime-based crucible of the present invention comprises 100 parts by weight of calcium oxide powder and 8 parts of calcium fluoride powder.
It is characterized in that a mixture with ˜30 parts by weight is press-molded into a crucible shape, and the obtained molded body is fired at a temperature of 1300 to 1550 ° C. until its apparent porosity becomes 12% or less.

As the calcium oxide powder as a raw material, a calcium oxide conventionally used as a raw material for producing a lime-based crucible, for example, a crushed product of sintered calcia clinker, electrofused calcia clinker, etc. can be used without particular limitation. . The raw material calcium oxide is 3 because of the above reason.
10 to 40% by weight of particles having a particle diameter of 1.0 mm to 0.5 mm and having a particle diameter of 1.0 to 0.5 mm and 0.15 m
It is preferably a powder containing 20 to 50% by weight of particles having a particle diameter of m or less.

As the calcium fluoride powder used as a raw material, fluorite powder that is commonly used can be used.
The calcium fluoride is preferably a powder having a particle size of 150 μm or less.

In the manufacturing method of the present invention, first, a crucible-shaped molded body is manufactured by press-molding a mixture of the raw material calcium oxide powder and calcium fluoride powder. The mixing ratio of the calcium fluoride powder to the calcium oxide powder is 8 to 30 parts by weight of calcium fluoride powder to 100 parts by weight of calcium oxide powder. Although it may vary depending on the firing conditions of the molded body, generally during the firing process of the molded body,
Although calcium fluoride tends to be decomposed and scattered, although slightly, it is preferable to use calcium fluoride in an amount slightly higher than the intended content of calcium fluoride in the lime crucible.

As the above-mentioned press molding method, the hydrostatic press molding method (rubber press molding method) can be conveniently used. Molding pressure is 800-1500kg / cm
A hydrostatic pressure of ² is sufficient.

In the production method of the present invention, the crucible-shaped molded product is then obtained at a temperature of 1300 to 1550 ° C. so that the lime crucible finally obtained has an apparent porosity of 12% or less, preferably. Bake until it becomes 8% or less. The firing time cannot be uniformly determined because it varies depending on the combination of requirements such as the composition of the molded body, the size of the molded body (especially the thickness), the firing temperature, and the apparent porosity of the target lime-based crucible. 15 minutes to 4 hours. In order to produce a lime-based crucible having a desired apparent porosity, an optimum firing temperature and a temperature depending on the composition of the molded product produced as described above, the size of the molded product (particularly the thickness), etc. Those skilled in the art can easily select the firing time.

[0035]

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Example 1 As calcium oxide powder,
Powdered calcia clinker (chemical composition, produced by calcination of calcium carbonate after firing at a temperature of 1800 ° C.,
CaO: 99.9% by weight or more, MgO: 0.02% by weight
Below, SiO ₂ : 0.01 wt% or less, Particle size: Particle size 3 m
10% by weight of m-1 mm, particle size less than 1 mm-0.5
20% by weight of mm, particle size less than 0.5 mm to 0.15
mm weight 30% by weight, particle size less than 0.15 mm 4
100 parts by weight (0% by weight) and 15 parts by weight of calcium fluoride powder (particle size: 0.15 mm or less) were thoroughly mixed using a ball mill to produce a uniform mixture. 1000 kg / c from this mixture using a rubber press
by press-forming at a hydrostatic pressure of m ^2, the crucible-shaped molded article (height: about 170 mm, the upper end outer diameter: about 87 mm, thickness: about 1
1 mm) was manufactured.

This crucible molding was placed at 1450 in a firing furnace.
Baked at ℃ for 50 minutes, lime crucible (height: about 150
mm, outer diameter of upper end: about 75 mm, wall thickness: about 10 mm). The apparent porosity of this lime crucible was 8.4%.

In the obtained lime crucible, granular sponge titanium (oxygen: 0.04% by weight, chlorine: 0.06% by weight,
Magnesium: 0.04% by weight) and high-purity aluminum particles (4N) are alternately filled (Ti: Al = 100: 5).
(2 weight ratio), and heated in a high frequency induction furnace at 1600 ° C. for 10 minutes to melt, and then cast into a mold and cooled. Obtained T
The oxygen content of the iAl-based alloy (measured by an inert gas melting infrared absorption method) was 0.11% by weight.

The oxygen content of the TiAl alloy obtained by repeating the same operation as above using the crucible used for melting the above TiAl alloy was 0.10% by weight. The oxygen content of the TiAl-based alloy obtained by repeating the same operation as above (third time) for the same crucible was 0.
The Ti content is 097% by weight, and the oxygen content of the TiAl-based alloy obtained by repeating the same operation as above (fourth time) is 0.
It was 066% by weight.

After the production of the TiAl-based alloy was repeated 4 times, no yellowing or damage was observed on the inner surface of the crucible.

Example 2 As calcium oxide, powdery calcia clinker (chemical composition, CaO: 99.9% by weight or more, produced by the same method as in Example 1),
MgO: 0.02% by weight or less, SiO ₂ : 0.01% by weight or less, particle size: 30% by weight having a particle size of 1 mm to 0.5 mm, 30% by weight having a particle size of less than 0.5 mm to 0.15 mm, 100 parts by weight of particles having a particle size of less than 0.15 mm (40% by weight), and the calcium fluoride powder 15 used in Example 1
Parts by weight in the same manner as in Example 1 and from this mixture using a rubber press 10
Press-molded with a hydrostatic pressure of 00 kg / cm ² to obtain a crucible-shaped molded product (height: about 170 mm, outer diameter at the upper end: about 87 mm,
Wall thickness: about 5 mm) was produced.

This crucible molded product was placed in a firing furnace at 1480.
Bake at ℃ for 30 minutes, lime crucible (height: about 150
mm, outer diameter of upper end: about 76 mm, wall thickness: about 5 mm). The apparent porosity of this lime crucible was 4.2%.

Using the lime crucible thus obtained, a TiAl alloy was manufactured in the same manner as in Example 1. The oxygen content of the obtained TiAl-based alloy was 0.079% by weight.

The oxygen content of the TiAl alloy obtained by repeating the same operation as above (second time) using the crucible used for melting the above TiAl alloy was 0.075.
%, And the same operation as above is repeated (3
Time) The oxygen content of the obtained TiAl-based alloy is 0.05
It is 8% by weight, and the same operation as above is repeated (4
Time) The oxygen content of the obtained TiAl-based alloy is 0.06
It was 6% by weight.

After the production of the TiAl type alloy was repeated four times, no yellowing or damage was observed on the inner surface of the crucible.

[Example 3] The amount of calcium fluoride powder used was changed to 20 parts by weight, and the firing conditions for the compact were 1480.
A lime-based crucible was produced in the same manner as in Example 1 except that the temperature was changed to 30 minutes. The apparent porosity of this lime crucible was 9.5%.

[Example 4] The amount of calcium fluoride powder used was changed to 10 parts by weight, and the firing conditions for the molded body were set to 1350.
A lime crucible was produced in the same manner as in Example 2 except that the temperature was changed to 90 ° C. for 90 minutes. The apparent porosity of this lime crucible was 11.3%.

Example 5 As calcium oxide powder,
Example 1 except that the particle size is 30% by weight with a particle size of 1 mm to 0.5 mm, 40% by weight with a particle size of less than 0.5 mm to 0.15 mm, and 30% by weight with a particle size of less than 0.15 mm. Using the same calcium oxide as used in, except that the firing condition of the molded body was changed to 1500 ° C. for 30 minutes,
A lime crucible was produced in the same manner as in Example 1. The apparent porosity of this lime crucible was 5.1%.

[Comparative Example 1] 15 parts of high-purity calcium carbonate
Among the pulverized products obtained by ball-milling the calcium oxide obtained by firing at 00 ° C. for 5 hours, the calcium oxide powder that passed through a 100-mesh Tyler standard sieve was used for 1200 kg / cm ² using a rubber press. Press molding was carried out under hydrostatic pressure to produce the same crucible-shaped molded article as in Example 1. This crucible-shaped molded product is placed in a firing furnace for 180
A lime-based crucible was produced by firing at 0 ° C. for 2 hours. The apparent porosity of this lime crucible was 5.8%.

A TiAl-based alloy was produced in the same manner as in Example 1 using the obtained lime-based crucible. The oxygen content of the obtained TiAl-based alloy was 0.12% by weight.
Met. Further, in this crucible, a crack was generated only by performing the melting operation of the TiAl alloy once, and the second T
It could not be used for the melting operation of iAl alloys.

From the results of Comparative Example 1, the calcium fluoride-free lime crucible cannot reduce the oxygen content in the metal or alloy after melting even if the apparent porosity is small, and the thermal shock It is clear that the resistance is also low.

[0052]

INDUSTRIAL APPLICABILITY The lime-based crucible of the present invention is capable of producing a metal or alloy having a low oxygen content, particularly Ti or TiAl-based alloy, without sacrificing the excellent heat resistance and corrosion resistance of the lime-based crucible. It is a lime-based crucible that has the outstanding effect of being able to

The lime-based crucible of the present invention, even if it is repeatedly used for melting a metal material, particularly Ti or TiAl-based alloy, does not infiltrate the molten metal into the crucible and is hardly damaged at all. Therefore, since it can be repeatedly used to dissolve the metal material, the lime-based crucible of the present invention can also be made thin, lightweight, and easy to handle.

Further, the lime-based crucible of the present invention can reduce the oxygen content in the metal material after melting, and further reduce the oxygen content in the metal material after melting by repeated use. It also has the effect of being able to do it.

Claims (2)

[Claims] 1. A lime crucible comprising 100 parts by weight of calcium oxide and 8 to 25 parts by weight of calcium fluoride and having an apparent porosity of 12% or less. 2. A homogeneous mixture of 100 parts by weight of calcium oxide powder and 8 to 30 parts by weight of calcium fluoride powder is press-molded into a crucible, and the obtained molded body is 1300 to 15 parts.
A method for producing a lime crucible, which comprises firing at a temperature of 50 ° C. until the apparent porosity becomes 12% or less.